<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        body {
            background: url(images/1.jpg) no-repeat center top;
        }

        li {
            list-style: none;
        }

        .baidu {
            overflow: hidden;
            margin: 100px auto;
            background-color: #fff;
            width: 410px;
            padding-top: 3px;
        }

        .baidu li {
            float: left;
            margin: 0 1px;
            cursor: pointer;
        }

        .baidu img {
            width: 100px;
        }
    </style>
</head>

<body>
<ul class="baidu">
    <li><img src="images/1.jpg"></li>
    <li><img src="images/2.jpg"></li>
    <li><img src="images/3.jpg"></li>
    <li><img src="images/4.jpg"></li>
</ul>
<script>
    // 1. 获取元素
    var imgs = document.querySelector('.baidu').querySelectorAll('img');
    // console.log(imgs);
    // 2. 循环注册事件
    for (var i = 0; i < imgs.length; i++) {
        imgs[i].onclick = function () {
            // this.src 就是我们点击图片的路径   images/2.jpg
            // console.log(this.src);
            // 把这个路径 this.src 给body 就可以了
            document.body.style.backgroundImage = 'url(' + this.src + ')';
        }
    }
</script>
</body>

</html>
